Electric control for machine tools



27, 1945. l s.'H. CALDWELL ET*- 238/9594 ELECTRIC CONTROL FOR MACHINETOOLS Filed Dec. 15, 1939 v6 Sheets-Sheet 1 lNvEN-roRs .1E Calda/ell JJJae er BY v 2% M TroRNEY l Nav. 27, 1945.

S. H. CALDWELL AETT AL ELECTRIC CONTROL FOR MACHINE TOOLS 6 Sheets-Sheet2 l Filed Dec. 15, 1939 ATTORN Y Nv'r.l27, 1.9.45. s; H. cLbwELL ErAL2,389,594

ELECTRIC CONTROL FOR MACHINE TOOLS Filed Dec. 15, 193s e sheets-sneu slaf/45E A PHASE B Nav. 2.7, 1945.

s.H.'cAA L.DwE| L ETA| 2,389,594 ELECTRIC CONTROL FOR MACHINE. TOOLSFilg; Dec. 15', 1939 e sheets-sheet 4 fai;

M n QW 'Um i N+ y ATTORNE Nav., 21, 1945;

s."H. ALDwry-:LLL ET AL. 2,389,594

ELEC'IRIC4 CONTROL FORHMACITIINE TOOL.:

6 Sheets-Sheet 5 Filed Dec. 15, 1959 Nov. 27, 1945. 's. HfALDwElL ETAL2,389,594

l ELECTRIC CONTROL -FOR MACHINE TOOLS V 6 Sheets-Sheet 6 Filed Dec. 15,193s INVENTORS ASE. Calda/ell ZJ J Patented Nov. 27, 1945 e 2,389,594 vELECTRIC coN'raoL Fon MACHINE 'rooLs Samuel H. Caldwell, Belmont, andJacob J. Jaeger, Cambridge, Mass., and Richard Taylor,

Great Neck, N. Y., .assignors to Niles-Bement- Pond Company, Hartford,Conn., a corporation of New Jersey Application December 15, 1939, SerialNo. 309,434

Claims.

This invention relates to metal cutting machines and particularly totracer controlledmachines adapted to cut irregular shapes such asbending and forging dies corresponding to a template or model thereof. I

An object of the present invention is to lprovide a machine generally ofthe Keller die sinking type '1n which a model of the die is mounted fortraversing by a tracer, the movements of the cutter over the work blankbeing controlled through thermionic means energized by slightdisplacement of a portion of the tracer during its traversing movements.

A feature of the invention that is important is that when the end of thetracer contacting the model is deflected slightly either laterally inany direction or axially backward, its movement serves to displace thepole piece of a pair of opposed electro-magnets and thereby unbalanceinduced voltages within windings of anl adjacent or interposed inductioncoil, the resultant'current within the last mentioned coil producedbythe speed of movement of the pole piece to an unbalanced position andby its unbalanced position being employed to control movements of thetracer and cutter relative to the model and work piece.

Another object of the invention is to provide thermioniccontrollingmachines for the speed and direction of rotationof oneor moremotors operating the moving slides for a diev sinking or similar metalcutting machine, the maximum speed of one of the motors being limited toa predetermined speed and the speeds. of the motors being controlledrelative to each other so that the tangential speed of the tracer overthe model and the cutter over the work piece may be maintainedsubstantially constant and at a. proper cutting speed.

More specifically the invention has for its main object-an improvedmeans and method for controlling the operative motions of theprincipalcomponent slides of a Keller type die sinking machineparticularly to enable these slides to move continuously but at variablespeeds in a manner to accurately reproduce a model and to operate atsuch speeds that maximum production may be accomplished.

With the above and other objects in' view, the invention includes thefeatures of construction and operationvset forth in the followingspecication and illustrated in the accompanying drawings.

In the accompanying drawings annexed hereto and forming a part of thisspecification, we have shown the invention embodied in one of thestandard types of Keller die sinking machines, but it will be understoodthat the invention can be otherwise embodied and that the drawings arenot to be construed as dening or limiting the scope of the invention,the claims appended to this specication being relied upon for thatpurpose.

In thedrawings:

Figure 1 is a front view in elevation of a die sinking machine of theKeller type on which the present Vcontrol mechanism has beenincorporated.

Fig. 2 is a side elevation of themachine shown in Fig. 1 with the workblank and model mounte in position for cooperation therewith. Y Fig. 3is a longitudinalsectional view of one form of tracer assembly employedin the control system and shown in relation to the,principal controlcircuits for the slide operating motors. Fig. 4 is a diagrammatic viewof the circuits for the tilt correction circuit indicated inl outline inFig. 3. y

Fig. 5 is a diagrammatic view of the circuits for controlling therelative speeds of the motors `for operating the tracer and cuttermoving slides.

Fig. 6 is a diagrammatic view of the circuits showing the control of thefollowing-motion motor from the displacement detector as shown in Fig. 3and forming a part of the tracer.

Fig. 7 is an enlarged view oflthe tilt detector forming part of thetracer assembly shown in Fig. 3. n

Fig. 8 is a longitudinal view of a modied form of detector adapted forindicating slight angular movements instead of axial movements as inFig. 7. y

- Fig. 9 is an end view of the detector shown in Fig. 8;- and Fig. 10 isa detail longitudinal view of the armature shown in Figs. 8 and 9.

In the above-mentioned drawings there has been shown but one principalform of the invention and a modied form of tracer component which is nowdeemed preferable, but it is to be understood that changes andmodifications may be made within thescope of the appended vclaimswithout departing from the spirit of the invention.

Briey and in its preferred aspect, the invention may include thefollowing principal parts: First, a machine having supporting means fora model and work blank and also supporting means for a tracer and acutter, there being operating slides provided on the machine so thatthere may be movements of the tracer and cutter relative to the modeland work piece respectively in the three directionsof rectangularizo-ordinates.

' toward and from the work may be made by the cutter over the work maybe controlled so that it is of any predetermined and constant amount.Control circuits hereinafter described operate two motors of the machineand each motor cony trois the movements of a slide. The tracer hasopposed electromagnets and a common pole piece extending axiallythereof, displacements of which energize circuits for these motors aswill pres` ently be more fully described, there being a controlsystemfor each motor so inter-locked that the maximum speed of the onemotor maybe limited and the two motors may be controlled to operate atrelatively different speeds.

Referring to Figs. l and 2 of the drawings, it will be seen that upon axed base I there is mounted a work 'blank W and a model or template Mdisposed directly above the work piece, both the work blank andtemplate,k being held rigidly iniixed position upon thebbase by anysuitable means not shown. Upon another portion of the base il andmovable horizontally therealong is a heavy column II which may betraversed in either direction along the base through a suitable screw I2and nut I3 connection by a motor Il hereinafter referred to as theleading motion motor drivinglv connected. to the screw I2 at one end. 0na vertical surface of the column II is slidably mounted a cutter head I5 suitably colmterbalanced and having therein a cutter slide i6 movablehorizontally toward and from the work blank W. Upon a bracket I1 fixedto and extending upwardly from this cutter slide Il is mounted the bodyportion of the tracer Il pomtioned for co-action with the model ortemplate M. As the above parts are standard construction for die sinkingmachines of the Keller type, it is not thought necessary to describethem more in detail. 'It will be sulcient to state that there is a motorI! preferably mounted on the horizontally movable cutter slide Ibymeansofwhichthecutterlmaybe rotated and that this cutter slide li may bemoved. towardand from the workplecewby ascrewZI, operated by a motor 23hereinafter referredto as the following motor.

Also there may be provided a third motor 2l for raising and lowering thecutterhead I5 upon thccolumn II butthismaynotusuallybecontrolledbythecircuits formingthepresentinvention and is employed more usually as afeed -mechanism to advance the cutter 2l to new traverslng positions atthe end of movements of thecolumn Il in either direction. If desired,however, the motor controlling the vertical D0-sltionofthecutrheadlimaybeedasa.leading-motionandthecolumnllmaybeadvanced slightlymorlnontally at theendof the sbohcofthecutterheadllineitherdirection tmdfcctthefeed.Intheembodimmtselected for illustration itwillbcassumedtlnt-themovementofthecolumnllalnngthebuellistheleadingmotionandthehorhontllmunmtof thecutterslide lltonnlandrmmthcwotkpiece W will be considered the following motion.

The tracer point 31, as seen in Fig. 3 when tilted by contact with a.model, causes motion of the tilt detector. The tilt detector establishesthe fact that contact with the model has been made, but does notinfluence the following or leading motions directly. If the slope of thesurface of the model being traversed is so small that the tracer pointreceives a considerable longitudinal component of force instead of beingtilted, it will be shown later that this force can cause correction totake place directly and without going through the intermediate stage ofcausing the tilt detector to operate. There is, however, a class of workin which the force required to move the tracer point 3l longitudinallyor axially is not available, but a tilting action is easily obtained,and this is the more general situation, which is to be described.

As soon as a tilt of the tracer point 31 occurs, a voltage is producedby the tilt detector dependent upon the amount of tilt produced, andthis voltage is introduced to an electrical circuit called the "tiltcorrection circuit (Fig. 3 and Fig. 4) in which it controls the actionof a thermionic tube 'which supplies power to a displacement solenoid"located within the main barrel of the tracer I8. When the displacementsolenoid 5l is energized, it withdraws an'lnner barrel 32 within thedetector, and in so doing, withdraws the tracer point 31 from the modelM by the amount necessary to cause the tracer point to reseat itself ina position parallel to the barrel of the tracer and also parallel to'the axis of the cutting tool. The motion produced by the energizing ofthe displacement solenoid 54 in straightening out the tracer point isalso transmitted to a second detector within the tracer, known as thedisplacement detector. 'I'he amount of displacement which pole piece 6Uof the displacement detector receives is the amolmt of motion whichwould have been produced if it were possible for the model to push onlylongitudinally on the tracerpoint without tilting it. Hence, the motionof the displacement detector is a true measure of the error in positionof the cutting tool at the instant of consideration. It is an importantobjective of the remainder of the control system to workwith as small aSignal of this type, that is, with minimum tilt or axial movement oftracer point 31, as possible so as to maintain a minimum error at alltimes.

for the moment, that the leading motion is continuing at a constantrate, the output voltage of the displacement detector is transmitted toa following-motion control circuit (Fla. 3A and Fig.,6). Within thiscircuit, present!! to be described more in detail, equipment is providedto control the torque, and; hence, the

' speed of the following-motion motor, so that the tracer point 31 willbe moved over the model with a minimum of error indicated in thedisplacement detector. Means are also provided in the combined action ofthe 'displacement detector and the following-'motion control circuit toimprove the precision of following by detecting the rate of change oferror and thereby anticipating correctlonsto the speed ol' thefollowingmotion motor. Y

AIt is an important desideratum of the control system that the workshould be followed not only wlthpreclsimbutalsoat suchspcedthatthccutting tool may at all times move thsentiall'yovcrtheslu'faceoftheworkatsua.

-talns a central cone.

vatomica.

.both the leading motion and the following motion, in order to reachthis objective.

In Fig. 3 pilot generators are shown schematispecification.`

cally on both the following-motion motor and leading-motion motor butwill be described more in detailas the description proceeds. Thesegenerators, rotating with their motorl armatures,

produce voltages proportional to the speeds of the motors to which theyare attached. The outputs of the .two pilot generators are transmittedas indicated. in this figure 4to a tangential speed control circuitwhere the two speed voltages are combined in a manner, and used toprovide bias voltages in thecontrols of both the followingmotion andleading-motion motors so that the tangential speed produced by the twomotors in v combination is substantially constant.

Another principal v'element of the Keller miachine is present in thissystem and that is the feed-motion motor. No special control of thisymotor is introduced, because it merely operates a fixed amount at theend of each cutting stroke. It should be pointed out, however, that anyof the three motors present` on the machine for moving the tracer andcutter in the directions of the rectilineal co-ordinates may perform anyof the functions of leading motion, the following motion or the feedmotion.

Referring to Fig. 3 of the drawings, the main assembly of the tracer iscontained within an outer barrel or sleeve 3|'. An inner barrel 32 isfree to slide within the outer barrel, and is sup'- ported by rollers33, which areL engaged by the flat plates 34, mounted on the innerbarrel. Normally, the inner barrel is pulled toward the left as viewedin this figure by the springs 35. `The amount of this motion toward theleft is limited by the engagement of a at plate 34 with a stop 38. f

The tracer point 31 is fitted upon and forms, in effect, an integralpart of the tilting spindle 38. The spring 39 presses the circular disc46 mounted on the spindle 38 against a projecting seat 4l permitting thespindle 38 to tilt about a pivot point located at any point upon theperiphery of the face of the plate 40. The tilting spindle 38 isprevented from rotating by means of the pin 42 slidable in a suitableslot.

At the extreme right end of the tilting spindle 38 is mounted theflanged piece 44 which con- The cone engages against a ball 45 whichrismounted in the end of the armature 46 of the tilt detector. The armature46 is constrained against sidewise motion by the bearings 41 and 48 andcan only move longitudinally against the action of the spring 49.

Hence, any tilting of the spindle 38 causes a lonn tains the cone ismade detachable from the spindle 38 and clamped thereon by the clampingscrew 50. By loosening the screw 58 and applying pressure to the rightend of the armature 46,

Ythe ball 45 will seat itself centrally in the cone and at the sametime, the plate ,40 will seat against seat 4l. The clamping screw can betightened while the assembly is thus aligned.

The armature 46 is surrounded by two excitation coils'il, '52 and a'pick-up coil 5 4, the action of which will be described at a later-.partof the A coil 54, hereinafter referred to as a displacement solenoid, iswound on a metallic bobbin 55, and located in the circular eld`structure consisting of the cylinder 56 and the two end plates .51 and'58. The armature 59 of the solenoid is drawn into the coil 54, that istoward the right as seen in Fig. 3, when the coil 54 is excited. The

pull of the displacement solenoid armature is transmitted by a pin 61 tothe shaft 6I which passes through a central hole extending through thesolenoid armature 59 and the displacement detector armature 68. Theshaft 6I is fastened to the end plate 68 Vof the inner barrel 32 andlocked thereto by the lock nut 62. When the spindle 38 tilts and causeslongitudinal motion of the armature 46, a voltage is induced thereby incoil 53 and this voltage is used to effect excitation of thedisplacement solenoid 54 which pulls on the solenoid armature 59,thereby pulling on the entire barrel 32 and moving the barrel and thespindle 38 back an amount necessary to' enable the tilting spindle 38 toregain a. seated position is fastened to the armature 59 of the solenoidwith a non-magnetic spacer piece 63 disposed between them. 'I'he spacerpiece 63 is introduced to prevent magnetic flux from solenoid armature59 passing into detector armature and thereby causing false indications.

The displacement detector is shown in the central portion of the tracercasingand has excitation coils 64 and 65 and a. pickup coil 66. Sinceth'e armature 60 of the displacement detector is mechanically coupled tothe armature 59 oi the displacement solenoid any motion of thedisplacement solenoid armature is directly transferred to thedisplacement detector armature. Since this motion is the amount oflongitudinal motion required to reseat the tilting spindle 38, it is ameasure of the longitudinal error shown by the position ofthe tracerpoint. displacement detector produces a, voltage proportional to its ownmotion, th'e output of the entire tracer assembly shown in Fig. 3 isavoltage proportional in magnitude and direction to the error shown bythe position of the tracer point 31. This statement is correct when A.C. excitation is applied to the coils 64 and 65 of the displacementdetector. If, as will be shown later, combined A. C. and D. C.excitation is applied to these coils, the output of the tracer assemblyin Fig. 3 is a voltage containing two components. The first is an A. C.component, proportional in magnitude and direction to the error inposition indicated by the tracer point 31. The second is a variablevoltage which is a'measure of the rate of change of the error asindicated by the tracer point.

If the slope ofthe portion of the surface of the model being followed byth'e tracer point is small, so that the tracer point is moved axiallyrather than tilted, the longitudinal motion is transferred directly tothe inner barrel 32 by way of the springs 39 and 49. 'I'his motion thenreaches the armature 60 by way of the rod 6I pin 61, solenoid armature59 and spacer 63. If the combined action of the springs 49 and 39 is notsufflcient to prevent motion of the spindle 38 relative to the barrel32, the result is a displacement of the detector armature 46. 'I'heresulting signal voltage acts just as though the detector motion was dueto tilting of spindle 38 and the dis- Since the placement solenoid willaid in producing the displacement.

Mechanical vibration of the movable parts is checked by the dash pot 88,containing the piston 18 mounted on the rod'8l. the dash pot iscontrolled by the screw 1|, which controls the size of the leakage pathbetween the ports 12 and 18.

Iiig 4 shows details of the tilt correction circuit. A primary 18 of atransformer 14 is excited from phase A and B of a three-phase circuit(see Fig. 6). Secondary coil 18 in series with a battery 'i1 suppliesthe excitation `coils 8| and 52 of the tilt detector. The pickup coil 58of the tilt detector delivers its signal to the grid circuit of the gastube 18. This grid circuit also receives an A. C. bias of adjustablemagnitude and phase obtained from the secondaryV windings 18 and 88 ofthe transformer 14. The magnitude of the grid bias is adjusted by thepotentiometer 8| and the phase is adiusted by the variable resistor 82and the condenser 83. The grid circuit oi tube 18, hence, consists ofth'e grid 84, the conductor 85, the pickup coil 58, the conductor 88,the potentiometer 8|, the conductor 81, the conductor 88, and thecathode 88. The cathode 88 of tube 18 may be heated by secondary 88 oftransformer 14. The plate circuit of tube 18 is supplied by the voltagefrom secondary winding 84 and consists of th'e plate 88, conductor 82,displacement-solenoid coil 54, conductor 8|, supply coil 84, conductor88, and cathode 88,

Theoretically the magnitude and phase of the A. C. grid bias obtainedfrom secondaries 18 and 80 should be adjusted so that, with no voltageproduced in the pickup coil 53, the tube 18 does not conduct. This isthe condition when th'e tilt spindle 38 is inA its undisturbed centralposition,

The electivenes of and under this condition no current flows in the ldisplacement solenoid coil 54. The A. C. bias in the grid circuit oftube 18 is furthermore adjusted as described in copending application ofCaldwell et al. Serial No. 290,404, led August 16, 1938. so that thevoltage induced in coil 53 by the primary coils 5|, 52 combines inproper relation with the bias voltage to cause tube 18 to conduct anamount of current approximately proportional to the voltage induced inthe pickup coil 58. The plate current of tube 18 thus controlled passesthrough the displacement solenoidvcoil 54, by which the barrel 82 of thetracer assembly is withdrawn and the spindle 88 caused to regain acentral position.

The A, C. bias from secondaries 18 and 88 is preferably adjustedexperimentally. It is necessary to cause motion of the solenoid amature88 by a very small voltage from th'e tilt detector. If the -tube 18 isinitially biased to non-conduction, internal mechanical friction willprevent the sensitive response desired. Therefore, the initialAabiasisadjustedsothatthetubeisslightly conducting, notV enough to causemotion or the armature 58, but enough to cause motion by a'verysmallincreaseotplatecurrentduetoa signal from the tilt detector.VThe excitation of coils 5| and 52 by a. combination of alternatingcurrent from secondary I8 and direct current from battery 11 isetfectedfor the purpose of producingavoltageinpickupcoilproportionaltothe velocity of the armature 48. Thisresults in' much more stable operation by making it pomble. for thedetector to anticipate motion of its armatureandthuscausealaroercurrenttoilowin the .solenoid cou u m order to preventexcessive Fig. 6 shows the circuit which places the 4fol-- lowing-motionmotor 28 under ldirect control of the displacement detector in thetracer assembly I8. Transformer 85 has its primary 88 excited betweenphase B and the neutral of a threephase alternating current powersupply. The secondary 81 in series with the battery 88 suppliesexcitation to coils 84 and 85 of the displacement detector. Due to thecombination of an A. C. and D. C. excitation, the output coil 88 of thedisplacement detector contains a voltage which is a measure of both theposition and the rate of change of position of the displacement detectorarmature 80.

The pickup coil 58 has a center tap 88. The

outer terminals of the coil 88 are connected to the control grids |00and 0| of'pentodes |02 and |08 respectively. The center tap 88 connectsthrough the bias battery |04 to the cathodes |05 and |08 of the pentodes|82 and |03 respectively. The cathodes of both pentodes are heated bythe winding |01 of transformer 85 by conventional connections which arenot shown. voltage supplied bycoil |08 o'f transformer 85 is impressedbetween the screen grids |08 and Ho and their cathodes |85 and |08. anda portion of the voltage from winding |08 is taken of! by means ofvpotentiometer (or by means of a tap on winding |88) and is appliedbetween suppressor grids ||2 and ||8 and cathodes |05 and |08respectively. The plate voltage of the pentodes is supplied by battery lI4 with the complete plate circuit as follows: starting at cathodes |05and |08, through conductor H5, through plate battery ||4,' through plateload reactances H8 and ||1 respectively, through conductors H8 and ||8respectively, to the plates |20 and |2| respectively of the pentodes |82and |08.

Considering the action of the circuit so far described, the voltagebetween the control grids |00 and |0| and their respective cathodes iscomposed of an A. C. voltage Proportional to the displacement of thetracer and a voltage varying from instant to instant with the speed ofthe tracer displacement. Due to the A. C. biases which are imposed uponthe screen grids |08 and ||8 and the suppressor grids ||2 and H8, thevoltages which appear across the load reactances ||8 and ||1 arecomposed of the original A. C. signal ampliiied, plus .the originalvariable voltage signal due to the D. C. excitation of the detector,amplied,'plus the original variable voltage,sig nal modulated at thefrequency of the A. C. voltages applied to the shield and suppressorgrids of the pentodes, plus distortion componentsl due to the tubecharacteristics, which do not aiIect the operation.

A The voltages just described appear between the terminals |22 and |28where they cause proportional currents to flow in the resistors |24 and|25. The condensers las and m are placed i acro the resistors |24 and|25 which serve to smooth out undesired high-frequency variations -whichmay occur; The grids |28 and |28 of the eter.|84, through conductor |85,through conductor |88, to the cathodes |81 'and |88 of the gas triodes.An A. C. bias is introduced in .the grldcircuitsoftubeo |88and |8|fromtheaecondarywindimzs |88'and148 oi transformer |4|.

AnA.C.'

'I'he condenser |42 and variable resistor |43 serve to adjust the phase"of the A. C. bias and the potentiometer |34 is used to adjust themagmtude of the A. C. bias. Winding |44 of the transformer |4| is usedto heat the cathodes of the two gas tubes. The primary winding |45 oftransformer |4| is connected between phases A and B of the three-phasesupply, and is so polarized that-there is a 30 phase angle between theprimary voltages on transformer 4| and transformer 95.

The plate circuits of the two gas triodes |36 and |3| are similar tothose described in the above-referred to copending patent applicationand include the secondary coils |54, |55 of the two .transformers |52,|53. The following-motion motor is a reversible repulsion motor, havinga. stator winding |46 connected between phases A and B of thethree-phase primary supply. The rotor 41 of this motor has two sets ofbrushes |48 and |49, which are connected to the primary windings |50Iand |5| of transformers |52 and |53 respectively. The secondaries |55and |55 of these transformers supply plate Voltage to plates |56 and |51respectively with the 4junction point |55a connected to the cathodes ofthe gas triodes.

With the armature 60 of the displacement detectcr shown in Fig'. 3 inthe balance position so that no A. C. voltage appears across the pickupcoil 56, and with the tracer point stationary, the voltage acrossterminals |22 and |25 is substantially zero. Under these conditions, theA. C.

'y biases on the grids ofthe gas triodes |30 and |3| are adjusted bymeans of potentiometer |35 and resistor |43 so that both tubes areslightly conducting. The plate voltages for these tubes are derived fromthe armature rvoltages across the brushes |48 and the brushes |49, andthrough the transformers |52 and |53. Since both gas triodes |30 and |3|are slightly conducting, substantially equal currents flow through bothsets of brushes on the following-motion motor, and the motor remainsstationary.

such direction as to prevent oscillation and overshoot of the followingmotion. If the error, that is the movement of the tracer from normal, isincreasing, the voltage proportional to the speed of the tracer pointwill be in the direction required to prevent further increase in error.If the error is decreasing, the voltage proportional to the speed of thetracer point tends to cause the error to decrease slowly, and hence,prevents a rapid movement through the zero error position which wouldcause overrunning and oscillation of the following motion.

The operating speed of the following-motion motor is primarily dependentupon the position and speed of the armature 55 of the displacementdetector. In operating on an actual machine, it is, of course, alsodependent upon the speed of the leading motion motor. Furthermore, it isdesirable to control the maximum speed of the following-motion motor andto relate the speed oi.' the following-motion motor relative to that ofthe leading-motion motor, so that the tangential speed of the tracerover the model and hence, of the cutter over the work, will besubstantially-constant. This control is described in connection withFig. 5, and ties in with the circuit diagram of if the armature 50 ofthe displacement detector K is moved slightly in either direction fromits balanced position, a voltage proportional in magnitude and direction(and also a voltage proportional to the speed of motion? is producedacross the terminals |22 and |23, and combines with the A; C. grid biasin the grid circuit of the gas triodes,

causing the grid voltage of one triode to shift,

in phase and magnitude in such a manner that its plate circuit conductsa larger current, and

causing an opposite change in the grid voltage of the other gas triode,so that its plate circuit conducts less plate current. There is, hence,a greater current caused to iiow in one brush circuit of the repulsionmotor than in the other, and the motor will rotate in the directiondetermined by which brush circuit is thus excited. If the armature '50of the displacement detector had moved in the opposite direction, thedirection of rotation of the rotor |41 would have been reversed.

Under this system of control, the amount of current ilowing in the platecircuit of whichever gas triode is conducting depends on the amount ofdisplacement of the armature 45I) of the displacement detector, so thatthe torque, and hence.-

also influenced 4by the speed at which the arma.

ture 80 moves. Furthermore, the signal produced by the velocity of thedisplacement detector is in Fig. 6 at the points |58 and |55, which arethe terminals of the conductor |35. Connection points |55 and |55 areindicated in both Figs. 5 and 6. Conductor |35 is shown solid on Fig. 6,since this connection is necessary for the operation of the circuit asdescribed up to that point. In Fig. 5, strap connection |35 is showndottedvbetween the points |55 and |59, indicating that when thetangential speed control circuit of Fig. 5 is used, the connection |55is removed, and point |55 on Fig.

5 is connected to point |55 on Fig. 6, and point |55 on Fig. 5 isconnected to point |55 on Fig. 6.

Referring to Fig. 5, the leading-motion motor is also a-repulsion motor(since it normally operates continuously in one direction, only one setof brushes is shown in use). The stator winding |55 of theleading-motion motor is excited'from phasesA andl B of the three-phasepower supply v shown in Fig. 6. The rotor |5| has brush sets |52 and|53, only one pair of which is used at one time. By means of adouble-pole, double-throw switch, not shown in the diagram, theconnections on brushes |52 can be switched to brushes |63 when it isnecessary to reverse the direction of the leading-motion motor at .theend of each cutting stroke. The rotor voltage ofv the leadingmotionmotor |||is applied to the primary |66 of transformer |55 and thevoltage thus induced in secondary |55 is applied between the plate |67and the ,cathode |58 of the gas triode |59. The grid circuitlof the gastriode |59 consists of the grid |15, the conductor |1|, thepotentiometer |12, the potentiometer |13, the conductor 1|, thepotentiometer |15, the conductor |56, the potentiometer ill, theconductor |15, the conductor |75 and the cathode |63. Potentiometer |`|5is used to supply part of the voltage of the battery as a D. C. bias inthe grid circuit. 'Ihe windings |8| and |32 of transformer |83 supply,under the control of condenser |34, variable resistor |85 andpotentiometer |11, an A. C. bias of adjustable magnitude and phase inthe above-described grid circuit of tube |69. .The primary |86 oftransformer |83 is supplied by phases A and B of the threephase A. C.supply in Fig. 6.

Rotating with the rotor Isl of the ieading-motion motor |4 is themultipole magnet |81 which j has its magnetic circuit completed by theyoke |38, and. by rotation, produces a voltage in the centerarmature ofthe rotor |6|.

- of torque as the speed builds up,

eventually reaches a maximum speed tapped pickup coil |89. This is thepilot generator shown attached to the leading-motion motor in theschematic drawing in Fig. 3, and is similar to the pilot generatordescribed in connection with the above-referred to application for amotor control system. The output voltage of the coil |89 is connectedacross the potentiometers |90 and I9I, and a portion of this voltage ispicked o by means of the slider assembly |92, and is applied across theplates |93 and |94 of the full-wave rectier |95. The cathode circuit ofthe rectifier |95 is completed by way of the cathode |96, the conductor|91, the potentiometer slider |98, part of the potentiometer |13, thepotentiometer |12, the conductor |99, the conductor 200, and then backlto the center tap of coil |89. Condenser is placed across the loadresistance of rectier |95, this load resistanceconsisting of all ofpotentiometer |12 and a portion of potentiometer |13, as determined bythe location of the -slider |98. The condenser 20| servesl to reduce thefluctuations of the rectified D, C. voltage across this load resistance.Due to rotation of the magnet |81, a voltage induced in coil |89 is thenrectiiied and appears across the load resistance of rectiiier tube|95'as a substantially D. C. voltage. It should be noted that the loadresistance of this tube |95 is also a component of the grid circuit ofgas tube |69, and this speed voltage is,

therefore, introduced in the grid circuit of the gasz tube |69.

Rotor |41 of the following-motion motor 23 motor, and causes a decreasein has a similar pilot generator mechanically rotated with it,consisting of the magnetic rotor 202, the. yoke 203, and the twocenter-tapped pickup coils 204 and 205. The output of coil 204 isconnected to potentiometers 206 and 201, and a portion of this voltageis picked oi by the slider assembly 208 and applied to the plates 209and 2|0 of rectier 2 I The cathode circuit of reatier 2|| is completedby way of the cathode 2|2, the conductor 2|3, the potentiometer |13, apor'- tioh of potentiometer |12, the slider 2|4. the conductor 2|5 andback to the center tap of the coil 204. Condenser 2|6 is connectedacross the load resistance of rectifier 2| I to smooth the rectifiedvoltage across the load resistance which, in this case, consists of allof vthe potentiometer |13 and that part of the potentiometer |12determined by the location of slider 2|4. It should be noted that thisload resistance is also in the grid circuit of gas tube |69. so that,due to rotation of the following-motion motor |41., a voltage is pickedupon coil 204, rectied in rectier 2|| and applied to the grid circuitofthe gas tube |69.

With neither the leading-motion motor I4 nor the following-motion motor23 rotating. the-bias voltages in the grid circuit of tube |69 areadjusted by means of potentiometers |15 and |11 and resistor |85, sothat the gas tube begins to conduct at the beginning of the positivehalfcycle of its plate voltage. Under these conditions, the rotor |5| ofthe exerts m'amum torque and begins to rotate. As its speed builds up.the voltage induced in coil |89 lincreases and, because of theconnections described above. introduces a rectiiied D. C. voltageproportional to the speed in the grid circuit 0f the gas tube |99. Thisspeed voltage is polarized in suchoa direction as to cause the platecircuit of the gas tube in the cycle and thus reducev the current in theDue to this reduction the rotor |6| which can |92, 208, |98 and 2|4 aremanner as to cause the leading-motion motor |4 |41 to appear in the gridcircuit oftube be controlled by the position of the slider assembly |92.The condition thus described is that required for the following of a,flat surface parallel to the plane of movement of the slide moved ybyleading motor I4 and which produces no mo tion of the tracer pointtowards or from the pat- I tern. This leading-motion motor I4 willsimply drive the cutter over the work at a constant speed, determined bythe setting of the slider |92.

If there is a change inthe shape of the model,

which causes a motion of the tracer point, the rotor |41 of thefollowing-motion motor 23 will turn at whatever speed is required tomaintain precision of the following motion. In doing so, it rotates thepilot generator magnet 202, induces a voltage in coil 204, which isrectiiied, and causes a D. C. voltage proportional to the speed of rotor|69. This D. C. voltage combines with the D. C. voltage produced by therotation of the leading-motion the speed of the leading motion motor |4.By adjustment of the sliders |92, 20B, |98 and 2|4. it is possible tocombine the contributions from the two pilot generators so that the sumof the squares of the speeds of: the leading-motion motor |4 and of thefollowing-motion motor 23 maintained substantially constant.v Underthese conditions, the tangential speed of the tracer and cutting toolover the surface of the model and the work, respectively, is at alltimes substantially constant, thus achieving one of the primaryobjectives of this invention. The relative adjustments of sliders alsoestablished in such to stoprotating entirely whenever the speed of thefollowing-motion motor 23` reaches a value which indicates that anextreme slope of the model is being followed. 1

Another voltage proportional to the speed lof the following-motion motor23 is produced in the coil 205 and applied to the potentiometers 2|1 and2|8. A portion of this voltage is picked oil by the slider assembly 2I9and applied to the plates 220 and 22| of the rectifier 222. The cathodecircuit of this rectifier 222 is completed from leading-motion motor toconduct at a later point the cathode 223, through conductor 224, throughresistance 225, through conductor 226, through potentiometer 221,through conductor 228, back to the center tap of coil 205. Condenser 229is connected across resistance 225 to smooth the rectiiied D. C. voltagewhich appears there.. Po-

tentiometer 221 introduces a part of the voltage v of battery 230inseries with the load circuit resistance 225 ofrectier 222. Thepolarity of battery 230 and the magniture of the voltage acrosspotentiometer 221 are adjusted so as to prevent any current from flowingin, voltage from appearing across resistor 225 until after the speed ofthe following-motion4 motor exceeds a. desired value, which isdetermined by the setting of the slider on potentiometer 221.

Therectied D. C.voltage across resistance 225 appears across terminals|58 and |58 in Fig. 5, as is described above. This voltage can beapplied to the like-numbered terminals. |53 and |59, in Fig. 6 byconnecting similarly-numbered points in the two iigures and removing thestrap conductor |35. The effect of this connection is -to introduce a D.C. speed control voltage in the and hence. any

speeds. but begins to act onlyat a speed deter; mined' by the magnitudeof the delay bias introduced from potentiometer 221 (Fig. andconstitutes means to prevent over-speeding `of the following-motionmotor' |4'| when considerable departure of the tracer point 21 from itsneutral position is experienced.

The winding 23| (Fig. 5) on transformer |83 is used to heat the cathodesof rectiflers |95, 2li and 222, by conventional connections, which arenot shown in the drawings.

In the above description one tracer assembly and tilt detector and themovable parts therein have been referred to generally and theiroperation has been explained. This tracer willv now be described indetail, particularly the tilt de tector referred to above and shown inan enlarged sectional view in Fig. 7. The armature consists of the shaft46, on which are mounted the cylinders or spools 258,259 and 262. Thesecylinders may be integral parts of shaft 46 or mounted in position onthe shaft. All parts of the armature and field structures are made ofiron or steel having suitable magnetic properties. The eld structureconsists of the disc 243, the ring 249, the discv0, the ring 25|, thedisc 252, the ring 253 and the disc 254 suitably clamped in alignment.The cylinders 258, 259 and 26|) on the armature are all of the samediameter and the central holes in the discs 248, 250 and 252 and 254 arein the particular embodiment shown all of another constant diameter.This arrangement forms a magnetic bridge which is excited by the coils5l and 52 previously referred to, and

coil 52 is the pickup coil, but the functions of these two sets of coilsmay be interchanged.

IThe armature is shown in its balanced position in Fig. '7, when thecentral cylinder 259 is symmetrically located with respect to discs 256and 252 and the cylinders 253 and 266 are symmetrically located withrespect to discs 24B and 254, respectively. Under these conditions, themagnetic fluxes, due to coils 5| and 52, pass radially inwardly in equalamounts through discs 256 and 252, across the air gaps 262 and 263 andthen longitudinally to the left and right-respectively through cylinder259, thence through shaft sections 265 and 266. These magnetic -iiuxesare balanced and thus no flux passes through cylinder 259.

It will be noted that cylinder 259 carries two components of magneticux, due to the coils 5| and -52 respectively, but these are polarized inopposite directions so that the resultant flux in cylinder 259 is thedifference between the two components. The balance point of the magneticbridge may now be definedv electrically rather than by its centrallyAdisposedrelation to the discs and rings 24s to 254 by saying that it isthe point at which the resultant flux through cylinder 259 becomes zero.Under these conditions,

the resultant flux linked by the pickup coil 53 is zero. y

If, now, the armature in Fig. 7 is moved slightly to the right, thereluctance of the air gap 263 between cylinder 259 and disc 252decreases and the reluctance of the air gap 262 between this cylinderand disc r25|! increases. As shown in Fig. 7, the reluctance of air gap26| between disc 248'and cylinder 258 will remain substantially constantwhile the reluctance of air gap 264 between disc 254 and cylinder 260will increase; by .using suitable dimensions for the cylinders 258 and260,'these air gaps may both be made to change with mechanical motionalso, so as to changes described when the armature is shifted.

slightly to the right, it will be observed that the flux due to coil 5lis increased, while the flux due to coil 52 is decreased and that aportion of the flux due to the coil 5| will pass radially inwardly ofthe plate 252 and return through the cylinder 259. The flux passingthrough the cylinder 259 is linked by coil 53, and a voltage is,therefore, induced in the latter coil. A voltage of opposite phase isinduced if the armature 46 is shifted in the opposite direction from itsbalance point.

The detector thus described may also be operated with combinedalternating and direct current excitation so as to produce a voltage incoil 52 which varies both with the position of the armature and with itsvelocity.

Referring now to the form of tilt detector shown in Figs. 8, 9 and 10 itwill be seen that in this form the detector operates by rotation of anarmature instead of by axial movement as in the f described inconnection with the detector described above. Coil B when used as theexcitation coil, is analogous to the vsource of electromotive force inthe conventional bridge, and coil A, when used as a pickup coil, isanalogous to the detector in a conventional bridge. The functions,however, of coils A and B may be interchanged.

If current is passed through coil B, magnetic flux is set up due to themagneto-force of the winding. Considering Figs. 8 and 9, one path whichthe magnetic ux will follow will be through the transverse yoke 242,upright piece 242, pole face 244 to the semi-cylindrical member 246, theupright piece 245 and back to transverse yoke 242. This is the pathfollowed at the left end of the armature and there willI be a similarpath for the flux at the right end of the armature in Fig. 8.

If the armature is in the position shownAin Figs. 8 and 9 so that equalamounts of the periphery of half-cylinder 246, as best seen in Fig; 10,are exposed to its pole faces 244 and 244B, the reluctances of its twoairgaps will be exactly equal because of the symmetry of thearrangement. When this condition holds, an exactly similar conditionholds at the opposite end of the amature in connection with secondhalf-cylinder 24|. Under these conditions the magnetic bridge is in abalanced condition and no magnetic ilux tends to pass along the armaturesection 236 which is linked by the coil A from one halfcylindricalportion to the other. Hence, no voltage is induced in the pickup coil A.

If the armature 238 is rotated by a slight amount, sayin the clockwisedirection, as viewed in Fig. 9, the reluctance of the air gap on oneside decreases and that of the air gap on the other side increases. Asimilar effect takes place at the opposite end of the armature, but in adiageach other have a decreased reluctance, because the half-cylinders240 and 24| are 180 out of phase, one with the other. Under theseconditions, the magnetic circuit becomes unbalanced, and part of theilux passes through the armature section 239 and returns through thelongitudinal yoke '246. The direction of the ux passing through section239 depends on the direction in which the armature 238 is rotated fromits balanced position. Since the armature section 239 is linked by thecoil A, a flux is induced in coil A directly proportional to the iiux inthe armature section 239. In practice, an alternating voltage is inducedin coil A because an alternating current is commonly used to excite coilB. rl'he voltage induced in coil A, with a constant alternating currentexcitation on coil B, is proportional to the amount oi mechanicalrotation of the armature 238 over a range which is suiilciently large tobe useful in the detection and measurement of small amounts ofmechanical motion.

The device as above described is applicable for detecting or 'measuringmechanical motion'of a tracer or other member when alternating currentexcitation is used. If, instead oi a simple alternating currentexcitation, a combination of alternating and direct current excitationis used, the same principles apply separately to both components of theilux which is produced. In measuring and detecting the angular positionof the armature 238, however, only the alternating current componentflux is effective in inducing a voltage in coil A, because the voltagethus generated must depend on the rate of change of flux linking thecoil. If, however, the armature is in motion instead of stationary, thevoltage induced in coil A will contain an alternating component whichwill vary with the instantaneous position of the armature and, inaddition, a voltage which varies as the angular velocity of thearmature. This is an extremely useful feature of the detector forapplication to automatic control of related motions. The combined A. C.and D. C. excitation may be produced either by mixing the two currentsexternally or by using two separate excitation coils instead of thesingle4 coil such as 'coil B, and applying A. C. excitation to one coiland D. C. excitation to the other.

There are certain classes of work in which a cutter is to be moved in anirregular path which may be satisfactorily accomplished by the automaticcontrol o! one motor only. That is, the motor 23 having its speed anddirection of rotation controlled by the tracer and the circuits shown inFig. 6 may be used for moving the cutter in one direction, while theleading-motion is accomplished by any ,manual or power-driven means,operating at a generally constant speedv 'and not requiring any of theelectrical control l mechanisms shown in Fig. 5 for the operation of theleading-motion motor I 8 I.

In the application of this portion of the pres-.- ent invention to amachine tool, the motion controlled by or from the tracer preferablywould result in movements of the tracer and cutter toward and trom themodel'and work blank. The motions of the cutter in the other directionsof rectilinear coordinates would be independently controlled in anydesired manner.

-What we claimis: A

1. A tracer controlled machine' tool having motor operated movablemembers, a tracer hav-- ing a tracer point movable in any direction, an.

inductive device electrically sensitive to movesaid tracer having atracer point movable in any direction, anA inductive device electricallysensitive to movement of said tracer point, means to apply a combinedalternating and constant excitation to said inductive device, motors formoving said members, and controlling means for at least one of saidmotors actuated by a resultant voltage of said inductive devicedependent partially upon the rate of change of displacement of saidtracer point and partially upon the distance moved by said tracer point.

3. A tracer controlled machine tool having motor operated movablemembers, a, tracer for controlling movement of one of said members, saidtracer having a tracer point movable in any direction, an inductivedevice having at least one coil and a pole piece moved relative to saidcoil by movement in any direction of said tracer point, means tocontinuously apply a combined alternating and constant excitation tosaid coil, motors for moving said members, and controlling means for atleast one of said motors actuated by resultant voltages in saidinductive device i induced by movements of said vpole piece.

4. A tracer controlled machine tool having motor operated movablemembers comprising in combination, a tracer body member, a tracer pointmounted therein for movement in any direction,.an electro-magnetic coilwithin said body member,- an induction coil adjacent said firstmentioned` coil, a pole piece within said coils movable in one directionby movement in any direction of said tracer point, whereby movement ofsaid pole piece induces voltages in said induction coil, means to supplya, combined alternating and constant excitation to said electromagneticcoil, whereby a resultant voltage will be induced in said induction coildependent partially upon the rate of displacement of said pole piece andpartially upon the distance moved by said pole piece, and circuitsenergized by said resultant voltage to control operation of one of saidmachine operating motors.

5. A tracer controlled machine tool having motor operated movablemembers comprising in combination, a tracer body 'member, a tracer pointmounted therein for movement in any di-S rectiOn, an electro-magneticcoil within said body member, an induction coil disposed coaxislly withsaid first coil, a p01e piece moved axially within said coils bymovement in any direction of said tracer point, whereby movement of saidpole piece induces voltages in said induction coil, means to supply acombined alternating and constant excitation to said electro-magneticcoil, whereby a resultant variable voltage will be induced in saidinduction coil dependent partially upon the rate of displacement of saidpole piece and partially upon the axial distance moved by saidpole-piece, and circuits energized by said resultant voltage tocontroloperation of one of said machine operating motors.

6. Atrscercontrolledmschinetoolhavingmotor' operated movable memberscomprising in combination, a tracer bodyA member, a ltracer pointmounted therein for movement in any direction, an electro-magnetic coilwithin said body member, an induction coil adjacent said first mentionedcoil, a pole piece within said coils movable in -one direction bymovement in any direction of said tracer point, whereby movements ofsaid tracer point and pole piece induce variable voltages in saidinduction coil, means to continuously supply alternating and constantexcitation to -said electro-magnetic coil whereby resultant voltageswill be induced in said induction coil dependent upon the displacementand rate of displacement of said pole piece, and motor operatingcircuits energized by said resultant voltages therein, and motors foroperating the machine tool members, one of said motors having itsdirection and speed of rotation controlled by said resultant voltage.

7. A tracer controlled machine tool having motor operated movablemembers, a tracer for controlling movement of one of said members, saidtracer having a tracer point movable in any direction, an inductivedevice electrically sensitive to movement of said tracer point andhaving at least one coil, means to apply a combined alternating andconstant excitation to said inductive device, motors for moving saidmembers, controlling means to limit the maximum speed of one motor, andmeans controlling the relative speeds of said motors actuated by theresultant voltage in a coil of said inductive device.

8. A tracer controlled machine tool having motor operated movablemembers, a tracer having a tracer point movable in any direction, aninductive-device electrically sensitive to movement of said tracerpoint, means to apply a combined alternating and constant excitation tosaid inductive device, motors for moving said members, controlling meansfor at least one of said motors actuated by a resultant voltage of saidinductive device, pilot generators coupled to said motors, and means toapply rectified voltages created by rotation of said pilot generators tolimit the current supplied to the armature of. one of said motors tolimit the speed thereof.

9. A tracer controlled machine tool having motor operated movablemembers, a tracer having a tracer point movable in any direction, aninductive device electrically sensitive to-movementof said tracer point,means to apply excitation to said inductive device, motors for movingsaid members, controlling means for at least one of said motors actuatedby a resultant voltage of said inductive device, pilot generatorscoupled to said motors, and means to apply rectiiied voltages created byrotation of said generators to limitthe maximum speed of one motor andto vary the relative speeds of both motors.

10. A tracer controlled machine tool having motor operated movable'members, a tracer having ya tracer point movable in any direction, aninductive device electrically sensitive to movement of said tracerpoint, means to apply a combined alternating and constant excitation tosaid inductive device, motors for moving said members,

controlling means for at least one of said motors actuated by aresultant voltage of said inductive device, pilot generators coupled tosaid motors,

and means to apply rectifietvoltages created by rotation of saidgenerators to limit the ma' mum speed of one motor and to vary therelative speeds Iof both motors.

11. A tracer controlled machine tool having motor operated movablemembers, a tracer having a tracer point movable in any direction, aninductive' device electrically sensitive to movement of said tracerpoint, means to apply excitation to said inductive device, motorsformoving said members, controlling means for at least one of saidmotors actuated by a resultant voltage of said inductive device, pilotgenerators coupled to said motors, and means to apply rectified voltagescreated by rotation of said pilot generators to limit the currentsupplied to the armature of one of said motors to limit the speedthereof.

12. In a control of the character described, a

tracer having a stylus displaceable positively and negatively from abalanced position, means for translating displacement of the tracerstylus in either direction from said balanced position into E. M. F. ofa magnitude depending upon the thermionic tube connected in the motorcircuiti to regulate the operation of the motor and governed by thecontrol circuit, and -an element driven by the tracer and through whichthe effecty of the control circuit on the thermionic tube is coordinatedwith the tracer displacement, means driven by the tracer for generatingan anti-hunt voltage the magnitude of which is proportional to the rateof tracer displacement, and means for applying the anti-hunt voltage tothe circuit to modify its effect on the thermionic tube and therebycompensate for motor lag.

.14. In a control for an electric motor; a tracer displaceablepositivelyl and negatively in either direction from a balanced position;a control circuit including a thermionic tube connected in the motorcircuit to regulate operation of the motor and governed by the controlcircuit; two sources of E. M. E. of variable magnitude connected withthe control circuit to supply control voltage theretracer displacementmodified by the rate of tracer displacement. 1 15. In a tracercontrolled machinetool having motor operated movable membersf' atracerhaving a stylus displaceable positively and negatively from a. balancedposition; means for translating displacement of the tracer stylus intoE. M. F. of

a magnitude depending upon the amount of displacement; means fortranslating displacement 0f the tracer stylu's into E. M. F. themagnitude of which is dependent upon the rate of tracer stylusdisplacement; motors for moving said members; and controlling'means forat least one oi said motors governed jointly by said two E. M. F.

SAMUEL. H. cALDwmL .moon J. Mmm.

RICHARD canon.

